Internal combustion engines inject hydrocarbons, i.e., fuel, into cylinders of the engine for combustion to generate power. However, not all of the hydrocarbons that are injected into the cylinders is combusted during the combustion cycle, and are expelled from the engine with the other exhaust gases. Additionally, some vehicles will inject hydrocarbons into the cylinders of the vehicle after combustion occurs, and/or into the flow of exhaust gas in an exhaust gas treatment system, to increase the concentration of hydrocarbons in the flow of exhaust gas. The hydrocarbons are injected into the exhaust gas in order to provide an exothermic reaction, which heats various devices of the exhaust gas treatment system for various purposes.
In order to produce the exothermic reaction, the hydrocarbons in the flow of exhaust gas require oxygen in the exhaust gas to react with. The amount of oxygen in the exhaust gas must be sufficient to react with the quantity of hydrocarbons in the exhaust gas, or some of the hydrocarbons will not combust, and may react with catalysts in the different devices of the exhaust gas treatment system, generating excessive heat within the devices. A vehicle controller may estimate the amount of oxygen in the flow of exhaust gas from the mass airflow and the estimated fuel injected into the engine. The vehicle controller may then control the amount of hydrocarbons injected into the flow of exhaust gas, based on the estimated amount of oxygen. However, if the measured mass airflow or the estimated fuel injected into the engine are incorrect, the vehicle controller may inject an excess quantity of hydrocarbons into the flow of exhaust gas, with insufficient oxygen to react with the quantity of hydrocarbons injected into the exhaust gas.